New York Natural Heritage Program
Black Tern
Chlidonias niger (Linnaeus, 1758)
Birds

Identifying Characteristics [-]
The total length of adults is 23-26.5 cm (9-10.5 inches). In breeding plumage the head and body are black, fading to gray on the rump while the undertail coverts are white. The upper surface of the wings and tail are dark gray, and wing linings are pale gray. The bill is black and feet are a dark reddish-purple. Females are somewhat duller than males, but this difference is often difficult to distinguish in the field. The postbreeding molt begins in late June when eggs begin to hatch. White feathers appear first around eyes and cheeks, then on forehead, neck, throat and breast, and finally on the abdomen. Heavily molting adults take on a peculiar, piebald appearance. The prebasic molt is completed during fall migration.

In winter plumage, the underparts are pure white except for a small, dark patch on each side of the breast and the back becomes a shade of gray similar to the wings and tail. A blackish cap joins black ear coverts on the otherwise white head. The juvenile plumage is similar to the winter plumage, but the feathers of the back are darker and the wing coverts and cap are barred and scalloped brown.

VOCALIZATIONS: shrill, somewhat metallic alarm notes, described as "kik" or "keek", depending upon intensity and level of motivation, and a complex of contact calls described as "kyew", followed by one to four additional syllables, as "kyew-dik", "kyew-dik-ik". The "kik" call commonly serves as a signal of impending danger in the nesting area. It may also be given during the ascent portion of the courtship flight. The "keek" call is similar to, but more shrill and forceful than the "kik" call, and is given during aggressive attacks on enemies in close proximity to the nest. The frequency of repetition increases as the terns become more aggressive. The "kyew" calls are given as parents approach and leave the nest, during foraging flights, by adults accompanied in flight by young, by parents calling to young at or near the nest, by parents at the nest during incubation, brooding and feeding, and during the courtship flights.

EGGS: ovate, ground color varies from dark olive to light buff with markings of dark brown and gray. Markings vary from small dots and scrawls to very large blotches and are often particularly heavy around the larger end of the egg. The average dimensions for 122 eggs in the U.S. National Museum were 34 x 24 mm (Bent 1921).

Nests are typically located in shallow water, close to open water or openings in stands of emergent vegetation. Nests are placed on heaps of floating vegetation, on old muskrat house, old grebe or coot nest, or on floating wood (Novak 1990). Floating mats of muck or algae, mud flats, and mud mounds and islands also have been used. The nest consists of a small gathering of aquatic vegetation with a simple, cup-like bowl (Weller and Spatcher 1965, Bailey 1977).

Characters Most Useful for Identification [-]
The overall dark coloration, highly acrobatic flight, and petite size (9-10", wingspan 2 ft.) distinguish this bird from other gull and tern species.

Best Life Stage for Proper Identification [-]
Adults in breeding plumage.

Behavior [-]
Black Terns are gregarious throughout the year and are considered a semi-colonial nesting species (Cuthbert 1954, Bergman et al. 1970). Nests may be clumped closely in favorable habitat or more widely scattered in less favorable areas. As is typical of colonial nesting gulls and terns, Black Terns will join together to defend the nesting area from intruders (Cuthbert 1954). Breeding colonies commonly change their locations if conditions become unfavorable (i.e., slight water level changes). Return rates may vary considerably among specific sites. Stern et al. (1985) found that 67% of recaptured terns nested within the same primary wetlands, while Bailey (1977) and Dunn (1979) reported return rates of 40% and 27% for marshes in Wisconsin and Ontario, respectively. These return rates, which are low in comparison with other gulls and terns, may be the result of the relative instability of their preferred habitat (McNicholl 1975). Conspicuous aerial courtship displays characterize the courtship period, which begins soon after arrival at the breeding site. In the "high-flight", a group of 2-20 terns ascend together to a great height then split into smaller groups of two or three and descend in rapid glides (Baggerman et al. 1956). During the "fish-flight", a male tern carries a small fish or large insect in its bill and is closely followed by a female as the two fly about the marsh. At the close of this aerial display the male follows the female to a perch and feeds her (Baggerman et al. 1956). Similar to some other marsh-nesting birds (i.e., Pied-billed Grebes), brooding Black Terns appear to leave their nest at night, leaving the eggs totally abandoned (Faber and Elbert 1996), or else the males incubate while females and non-breeding males spend the night at communal roosts up to 2-3 km away (Custer and Custer 1996). Eggs in abandoned nests had high levels of Organochlorine contaminants in them suggesting this may have played a role in this behavior. Black Terns' overall low reproductive rate (< 1 chick fledged/pair), and low nest success rates (<50%) are often attributed to nest predation, but in some ways may be related to this nocturnal brooding behavior. In order to compensate for such low reproductive rates, Black Terns are relatively long-lived for a bird (~8 yr.) and adults have comparatively high annual survival rates (Dunn and Agro 1995).

Diet [-]
On the breeding grounds Black Terns are primarily insectivorous, although small crustaceans, spiders and small fishes are also regular food items (Bent 1921). The diet may vary depending on habitat and food availability. Fishes may be an especially important food item especially in terms of biomass. Small fish appear to be critical for chick development since chicks cannot develop on insects alone and fish are a key source of calcium. In waters devoid of adequate fish prey calcium deficiency leads to malformation and death in chicks (Bientema 1997). In Maine, Gilbert and Servello (2005) found that chicks could develop normally on insects and/or fish alone, but that the availability and choice of food may affect adults more so than chicks. Because of their higher biomass and nutritional value, adults primarily feeding fish to chicks may have to spend less time and energy feeding the young with positive consequences for their own condition, survival, and future breeding success. The capability to use both fish and insects may reduce potential variability in food availability during the breeding season (Gilbert and Servello 2005). In wetlands, food is captured in the air, at or just below the water surface, and from the surface of emergent vegetation (Goodwin 1960). In the prairies, much of the food is obtained from plowed land and fields of grain but foraging over agricultural land near marshes has rarely been observed in New York (Novak 1992). In a sample of 376 feedings of young in different nests at North Pond in New York, Goodwin (1960) found that 41% of the items brought by parents were minnows and 59% were insects, including 45% damselflies. Insects comprised 93.6% of 602 feedings to chicks in Michigan while fishes accounted for just 4.9% (Cuthbert 1954). Although many of the insects could not be identified, damselflies, dragonflies, and mayflies were important food items. One study reported that 46 damselflies per hour were fed to chicks (Dunn and Agro 1995).
Black Tern Images
click to enlarge
The Best Time to See
Black terns typically arrive from their South American wintering grounds in early May and begin actively searching for suitable nesting marshes. June is the prime nesting season, but nesting often extends into mid-July. Young of the year are in the air and feeding with adults in late July and August, and the birds begin departing by September. In the northeastern U.S., egg laying begins in late May, but may be initiated as late as the middle of July. Nests with eggs were observed at one site in western New York from 24 May to 12 July (Firstencel 1987). During a 1989 survey of colonies throughout New York, nests with eggs were observed as early as 25 May and as late as 18 July (Novak 1990). Black Terns are not known to be double brooded so later nests probably represent renesting attempts; and they can renest up to 40 km away (Muller and Roggie 2001).

Spring arrival seems to have advanced by about a month since the turn of the century. Eaton (1910) reported that Black Terns typically arrived around the first of June and nested in July.
J F M A M J J A S O N D
Present Breeding
The time of year you would expect to find Black Tern present (blue shading) and breeding (orange shading) in New York.
Similar Species
  • Common Tern (Sterna hirundo)
    The Common tern is much lighter in overall coloration with a heavier orange (not dark) bill and larger size.